Ball Transfer

If you have a differentially steered robot, it is useful to use a ``ball transfer'' as the third support point. A ball transfer is basically a ball that can rotate in any direction at any time. This is better than a wheel that swivels, especially for in-place turns. A wheel that swivels will skid and introduce errors.

You can purchase ball transfers from industrial places that make/sell ball transfers for transfer table applications. Such ball transfers are made from steel and can be quite large and heavy. They work well with a heavy robot, but lighter robots cannot even exert enough force to get the ball to rotate.

Another option is to buy some inexpensive plastic balls (from a local plastic supplier, such as TAPS in Sacramento, CA), and somehow hold the ball in with plastic material. One student of mine was very creative and purchased a pair of measuring spoons with half-sphere scoops that match the size of the plastic ball. In this case, make a hole to expose the plastic ball, use rubber band to hold the two spoons together and you have an inexpensive and light ball transfer!